Producers should be on alert for damage from army worm as they have been found in large numbers in north Missouri this week.

True armyworms over winter in Missouri, but both true armyworm and fall armyworm moths migrate into the area during storms that move in from the south.

Common host plants include tall fescue or other forage grasses, alfalfa and corn. Scout in the early morning or late evening for the best chance of seeing small larvae since they feed on the lower leaves of the plants at those times. Larger larvae will feed higher on the plant and during daylight hours. The larvae grow to about 1 Â½ inches in length. True armyworms are greenish-brown in color with a pale stripe running the length of their back and an orange line running their length on each side. The head is light brown and the body is smooth and hairless. The larvae will have a brown triangle on the outside of each of the four pairs of legs in the middle to back of their body. During late summer fall armyworms will be dark to completely black in color with stripes running the length of their body and an inverted Y on the face of the worm. Four spots or bumps will be found on each segment. The bumps will be arranged in a square pattern on the last body segment.

Treat for true armyworm in pasture and hayfields when there are four or more worms present per square foot. Fall armyworm treatment is warranted when there are three or more worms per square foot. Be sure to follow label restrictions for harvest or grazing intervals when applying insecticides.

For more information contact your local University of Missouri Extension office. University of Missouri Extension programs are open to all.